1. Field of the Invention
The invention relates to vehicle bumpers. In one aspect, the invention relates to a stamped folded vehicle bumper beam. This application claims priority of provisional U.S. Patent Application Ser. No. 60/302,534, filed Jul. 2, 2001.
2. Description of the Related Art
Bumpers are an integral part of any motor vehicle. The primary function of a bumper is to absorb and distribute impact loading during a collision, thus providing an important safety feature of the vehicle. While a bumper can assume a variety of configurations for providing the safety function, it is desirable that the shape of the bumper conform to the overall styling of the vehicle. Additionally, reducing the bumper weight is an important consideration in meeting fuel efficiency standards.
Bumpers have traditionally been roll formed or stamped from a single blank of material such as steel, and are rigidly attached to the vehicle frame. A roll formed bumper generally takes the shape of an arch with the apex of the arch facing forward toward the direction of travel. The bumper absorbs impact loading through the deformation, i.e. flattening, of the arch. However, flattening of the bumper under impact loading will tend to push the vehicle frame elements outward, thus causing considerable structural damage. Resistance of the bumper to deformation under impact loading is generally a function of the size, shape and strength of the material forming the bumper. Since the strength of the bumper is directly related to its size, it is difficult to obtain a bumper of sufficient strength while at the same time minimizing its weight and thus improving the vehicle's fuel efficiency. Furthermore, roll formed bumpers are typically mounted to the end of the vehicle frame elements, which involves a bumper-to-frame connection which has somewhat less rigidity and strength than a connection which is set back from the end of the vehicle frame elements. Mounting the roll formed bumper to the end of the vehicle frame elements effectively moves the bumper significantly forward of the vehicle chassis with resulting limitation on the vehicle aesthetic design considerations.
One such design consideration is impact performance. It is preferable that the front beam meet vehicle manufacturer specifications, such as managing a bather and a pendulum impact, without damaging adjacent systems.
Other important considerations involve noise, vibration, and harshness (NVH) considerations. The front beam is the first cross member of the vehicle frame and is an integral component of front end frame characteristics. The bumper beam design must also accommodate studio design constraints, which can include such aesthetic characteristics as a highly swept front end and an increased frame length of the front rails for improved crash performance.
Since the top surface of the front bumper beam can be visible in a lower air opening for the vehicle front end, the appearance of a bumper should meet design studio intent for a styled and integrated look with the front fascia for the bumper. In addition, the front beam cannot affect air intake for engine cooling by interfering with airflow in the lower air opening.
Past attempts to solve these functional and aesthetic design constraints have fallen short. One such past prior art attempt was to form the bumper beam as a roll formed beam with a B-shaped cross-section therein. This B-section roll formed beam was attached to a bracket welded to the end of the frame rails. The roll form beam could not meet several of the design objectives. First, the beam could not meet the sweeped appearance required for vehicle aesthetics, it could not accommodate the extra length of the frame rails, and it was positioned relatively high in the lower air opening, which affected both air intake and appearance.
Another past attempt was to form the bumper beam as a roll formed beam with stamped end cap portions. This second attempt included a roll formed section welded to two stamped end caps. The end caps would accommodate the sweep and extra length of the frame rails, but the roll form center section was still visible in the lower air opening of the vehicle.
Another prior art bumper was formed as a stamped open section with a back plate welded thereto to form a closed section beam. While this option proved least costly to manufacture, it was still desirable to reduce the number of parts and forming operations for a fully functional, high-strength and aesthetically-pleasing bumper design.
Further prior art attempts included a hot stamping process to form the bumper beam that proved costly to manufacture but can achieve the higher strengths needed in bumper applications. One standard option for this prior art system of this type was to form the bumper beam out of roll formed B-sections and box sections which include a swept bumper portion to satisfy aesthetic requirements. Ultra high strength steel was used to form this beam and also employed EPP filler pieces to match geometry of whatever bumper fascia assembly was employed.
This stamping prior art process achieved its strength through the use of geometry of the bumper beam cross sections, ultra high strength steel, and the sweep curvature of the bumper. Because this is still a roll formed bumper assembly, this process did not allow the bumper beam to fit closely to the vehicle and include bumper fascias with multiple geometry features as required for many bumper systems. Finally, these types of bumper systems that include swept roll formed sections also include an open arch geometry or a curved beam. When a front centerline impact is encountered, the impact force works to flatten these swept sections out. As a result, the only features of this prior art design resisting this impact force are the strength of the bumper beam material and the vehicle frame rails.